In a high-speed serial interface adopted in a back end of a storage system, such as a SAS (Serial Attached SCSI) or a PCI-express (registered trademark, hereinafter referred to as PCIe), speeding-up of a data communication by speeding-up of a transfer speed, and configuring one logical transmission line by collecting a plurality of input/output ports such as a multi-lane or a multi-link.
Such high-speed serial interface is a method which flows a differential signal corresponding to encoded data, on a signal transmission path generally taking two lines as one pair. Further, in an evaluation of a signal quality of such high-speed wiring, a method of measuring an eye pattern of an overlap of the differential signal, which is displayed on a display of a signal measurement instrument, is used. Generally, it is desirous that an opening area of the eye pattern is large, and a cross point of the differential signal is positioned at an intermediate potential of both signals. As one method of forming the signal transmission path and wiring of the differential signal, there is disclosed a technique of Patent Document 1.